Electrical signal receiver



May 8, 1934.

T. LAURENT ELECTRICAL S IGNAL RECEIVER Filed Dec. 22, 1927 Patented May8, 1934 PATENT OFFICE ELECTRICAL SIGNAL RECEIVER ,TorbernLaurent,Stockholm, Sweden, assignor to 'lelefonaktiebolaget L. M. Erlcson,vStockholm, Sweden, a company of Sweden Application December 22, 1927,Serial No. 241,979 In Sweden January 4, 1927 9 Claims.

The invention relates to electrical signal receiv ers, particularlyringing signal receivers for use in connection with long distancetelephone r lines provided with amplifying translators. 'In sendingringing signals, for instance calling and clearing signals, over suchlines ringing currents of audio frequency are preferably'used as suchcurrents may be passed through and amplified in the translators withoutany additional auxiliary means being required for that purpose. Ageneral condition for the construction of such receivers is that thereceiver shall operate reliably for ringing currents of a certain audiofrequency while being unaffected by ordinary speech currents. Thepresent invention has for its object to provide a signal receiver whichfulfills this condition in a more perfect manner than has been possibleheretofore and which is capable of being connected up between the twobranches of the telephone line, directly or through a transformer, atany point desired.

The invention is based on the following principles. The signal receivershould operate for a current of a pure audio frequency which as to thevalue of the frequency and the incoming energy as well as its durationis confined within certain limits. With a view to securing a reliableand efficient service said limits should be rather spacious.Considering, however, that the frequencies occurring in speech maymomentarily meet the said conditions for the ringing signal current, itwill be necessary to take measures for preventing disturbances by thespeech. This is realized according to the present invention by providinga blocking device responding to currents of audio frequency other thanthose covered by the ringing signals and adapted to put the Signalreceiver in an inoperative condition. The operation of this blockingdevice is based on the fact that such tones of the speech which are mostapt to affect the signal receiver, are never quite pure and, moreover,are of a very short duration in the course of ordinary speech. The factlast mentioned is taken advantage of by constructing said blockingdeviceand the signal receiver so that the former will respond more quickly tothe speech currents than the latter, whereas, after having once beenmade operative, it will be slow to regain its inoperative condition. I50 The invention will be more closely described with reference to theaccompanying drawing which illustrates three different circuitarrangements for a signal receiver.

Fig. 1 is a circuit diagram of the first embodiment.

Figs. 2 and 3 are corresponding circuit diagrams of the 2nd and the 3rdembodiment respectively.

In Figure 1, the circuit of the signal apparatus 1 is controlled by tworelays 2, 3, included in the anode circuits of two rectifying valves 4,5 69 respectively the grid circuits of which include the secondarywindings of transformers 6, 7 and grid potential batteries 8, 9respectively. The primary windings of saidtransformers are connected inseries in the anode circuit of an amplifier valve 10 the grid andcathode of which are connected to the terminals 11, 12. By means of abattery 13 the grid of the valve 10 will obtain a potential adapted tocause the valveto operate only as an amplifier. A. battery 14. furnishesthe current for the anode circuit. Bridged across the primary windingsof the transformers 6, '7 are resonance shunts 15, 16 respectively,which are both tuned to the frequency of the signal current. The shuntis a potential shunt having an inductance and a capacity connected inparallel, whereas 16 is a current shunt having an inductance and acapacity connected in series. The transformer 7 and the appertainingcircuits constitute a blocking device adapted 81? to make the receiverinoperative to currents of signal frequencies occurring in the speech.

The signal receiver is adapted to be connected up to the telephone lineby the terminals l1, 12, being connected each to a branch of the line.$5 A signal current sent over the telephone line will then produce analternating current potential in the secondary winding of thetransformer 6, causing the relay 2 to operate and to close the circuitof the signal apparatus 1 at the W contact 1'7, whereas the relay 3remains unoperated owing to the shunt 16 acting as a shortcircuit to theprimary winding of the transformer 7 for currents of the signalfrequency. For currents of other frequencies, for instance speech 5currents, an alternating current potential will, however, be generatedin the secondary winding of the transformer '7 so as to cause the relay3 to open its contact 18, thus preventing the signal apparatus to beoperated by momentarily 10% occurring speech currents of suchfrequencies that otherwise might be able to cause an operation of thesignal apparatus. This operation of the blocking device depends upon thefact that speech currents are never of a pure frequency and said devicewill therefore practically operate for all speech currents includingthose which are most, apt to produce a false signal, provided the relay3 is sufiiciently sensitive. The same result can be obtained quite apartfrom the said speech currents.

operation of the blocking device by making the relay 3 slow to releaseits armature so as to keep its armature attracted during the shortintervals of the speech when currents of signal frequency or about thatfrequency occur. Evidently, said methods may be arranged to cooperatefor the purpose'aimed at. It remains to consider the operation of thereceiver at the very moment when a wave train of speech currents ofsignal frequencies enters the receiver and when both relays 2, 3 arestill unoperated. At this moment the shunt 15 will at first act in knownmanner as a short-circuit, whereas the shunt 16 will act as a greatresistance. As a consequence, the blocking device will enter intooperation and will open the contact 18 in the signal circuit before therelay 2 attracts its armature, thus preventing false signal also in thisparticular case. Said action being due to the influence of the front ofthe incoming wave it will take place both for signal currents and for Incase of signal frequencies the conditions are reversed after theincoming waves have developed normally in the shunts 15 and 16, so thatthe shunt 15 will then offer a great resistance to the currents, whereasthe shunt 16 acts as a short-circuit thus producing the conditions firstabove described. The same result may, of course,. be obtained by makingthe relay 2 slow to attract its armature. An important feature of theblocking device is, therefore, that it shall be quick to enter intooperation and relatively slow to regain inoperative condition.

The use of slow-acting relays 2, 3 may be unsuitable in someapplications of the invention. This inconvenience is, however, overcomein the circuit arrangement shown in Figure 2. In this arrangement thecircuit of the signal apparatus 1 is controlled by a single relay 19,included in the anode circuit of a valve 20. The grid circuit of saidvalve includes a grid leak 21 shunted by a condenser 22, and twobatteries 23, .24, supplying a negative grid potential of such a valuethat the anode current is practically zero in the normal or in operativecondition of the receiving device. Inserted in the secondary circuit ofeach transformer 6 and 7 is a glow lamp 25 and 26 respectively such as aneon lamp having builtir. resistances 27 and 2.8 respectively. Insteadof neon lamps any discharge gap capable of independent discharge may beused. The secondary winding of the transformer 6 is connected at one endto the grid of the valve 20 through the neon lamp 25 and. a resistance27 and at the other end to the positive pole of the neon lamp battery23. The secondary winding of the transformer 7 is connected at one endto the grid of the valve 20 through the neon lamp 26 and resistance 28and at the other end to the negative pole of another neon lamp battery29. The voltage of the neon lamp batteries is not itself sufficient tocause glowing of the lamps, which therefore normally act asinterruptions in the secondary circuits of the transformers. The voltagegenerated in the secondary circuits by the signal and speech currentswill, however,

- cause the lamps to glow thereby establishing a conductive path throughthe lamps. Thus, when glowing, the lamp 25 will connect the grid of thevalve 20 with the positive pole of the battery 23 and the upper plate ofthe condenser will obtain a positive charge, whereas the lamp 26 willsupply a negative charge by connecting th grid with the negative pole ofthe battery 29. The blocking circuit will therefore, evidently, striveto neutralize the action of the signal current has ceased the condenser22 will dischargev through the leak 21 and the valve 20 will be restoredinto its normal condition. v

If currents of other frequencies than the signal frequencies, forinstance the speech currents, enter the signal receiver, the transformer7 will come into operation causing the neon lamp 26 to glow whereby theupper plate of the condenser 22 will be charged negatively from thebattery 29.

The valve 20 will consequently still allow no anode current to passthrough it. If during this condition speech currents of such frequencieswhich are apt to cause operation of the signal apparatus, would enterthe receiver, the glow lamp 25 would operate to supply a positive chargeto the .condenser 22. It will be found, however, that in speech thenegative charging is favoured to such an extent in preference to thepositive one that the latterwill never predominate. This result issecured chiefly by the fact that the condenser 22 is relatively slow todischarge through the leak 21 and its negative charge w'll therefore bepreserved till frequencies other can the signal frequencies againpredominate. The condenser 22 should preferably be of such capacity soas to be charged by a small amount of energy, and the leak 21 shouldhave such a resistance as to produce the slow action in the discharge ofthe condenser required for a reliable operation of the device. Theaction of a'.wave front is the same in this circuit arrangement as inthat of Figure 1. Thus upon a wave train entering the receiver theblocking circuit will become operative more quickly than the signalcircuit. The sluggishness of the signal circuit at this instance can beincreased, if necessary by introducing an additional resistance inseries with the glow lamp 25. The arrangement according to Figure 2 hasthe further advantage that disturbing currents, the energy of which isgenerally rather small, have no influence on the signal receiver at allas such feeble currents are unable to cause the gleamlamps to gleam.

In the modification shown in Figure 3 the potential generated in thesecondary circuit of the transformer 6 influences directly the grid ofthe valve 20 instead of being used to charge the condenser 22positively. It will be seen from the circuit diagram that the secondarywinding of the transformer 6 is then connected up between the grid andthe condenser 22, no neon lamp being used in the signal circuit.Otherwise the circuit arrangement is substantially the same as in Figure2. The alternating currents generated in potentials in the transformer 8that may occur. This arrangement oflers the possibility of using an.alternating current relay 19 tuned to the modulating frequency of .amodulated signal current,

for instance a 500-period current modulated with terns where a ringingsignal is-sent over a wire connection as in the examples described abovebut may be used generally for wire or wireless systems. 'In both casesthe ringing signal cur-- rents may be transmitted with or without theaid of a carrier wave.

Iclaim:

1; A receiving devicein an electric communication system comprising incombination a signalling circuit adapted to select signallingfrequencies within a certain frequency range, a blocking circuit adaptedto be passed by currents of other frequencies than the signallingfrequencies, a valve device, signalling means controlled by'said valvedevice, means connecting the grid circuit of the valve device with thesignalling circuit and means connecting the grid circuit of the valvewith the blocking circuit in such a manner as to make the valveinoperative upon energization of the blocking circuit by such currents.

2. A receiving device in an electric communication system comprising incombination a signalling circuit adapted to select signallingfrequencies within a certain frequency range, a

blocking circuit adapted to be passed by ourrents of other frequenciesthan the signalling and the blocking circuit in such a manner as tocause the condenser to be charged with different polarities by currentspassed through the signalling circuit and the blocking circuitrespectively.

3. A receiving device in an electric communication system comprising incombination a signalling circuit adapted to select signallingfrequencies within a certain frequency range, a blocking circuitadapted-to be passed by currents of other frequencies than thesignalling frequencies, rectifying discharge devices in said circuits, avalve device, signalling means controlled by said valve device, acondenser included in the grid circuit of the valve device, meansconnecting the condenser with the signalling circuit and the blockingcircuit in such a manner as to cause the condenser to be charged withdifferent polarities by currents passed. through the signallingcircuitand the blocking circuit respectively.

4. A receiving device as claimed in claim 2,

characterized by the said condenser being arranged to be charged bycurrents in the signalling circuit so as to make the valve operative.

5. A receiving device as claimed in claim 2, characterized by the saidcondenser being arranged to be charged by currents in the blockingcircuit so as to make the valve inoperative.

6. A receiving device as claimed in claim 3, characterized by thecondenser being charged through a glow lamp which is caused to glow bythe action of the currents in the blocking cir-' cuit and the signalcircuit respectively.

'7. A receiving device as claimed in claim 3, characterized by'thecondenser and a leak resistance shunted thereto being included in boththe signal circuit and the blocking .circuit, in each of which they areconnected in series with a glow lamp and a glow lamp battery.

8. A receiving device as claimed in claim 3, in which a resistance isincluded in the signal circuit or the blocking circuit to retard thecharging of the condenser.

9. A receiving device as claimed in claim 3, in which the dischargedevices are adapted not to be brought to discharge by feeble currentssuch as disturbing currents. v

TORBERN LAURENT.

